The present invention relates to improvements in metal diaphragm valves for use in semiconductor manufacturing apparatus and others.
A diaphragm valve of this type is known from unexamined Japanese patent application laid-open under No. 8-105554, for example.
As shown in FIGS. 4 and 5, the metal diaphragm valve 20 comprises a body 25 having a valve seat 24 at a bottom face of a valve chamber 23 communicating with an inflow path 21 and an outflow path 22, a metal diaphragm 26 having an upwardly bending central region and being provided in said body 25 in such a manner that the valve chamber 23 is sealed in an airtight fashion, driving means 27 that are operable to press the metal diaphragm 26 against valve seat 24 and to allow the metal diaphragm 26 to return elastically to its original shape and move away from valve seat 24 and a ring-shaped groove 28 that is formed under the valve chamber 23 in communication with said outflow path 22.
Owing to said ring-shaped groove 28 the metal diaphragm valve 20 shown FIGS. 4 and 5 can allow a large quantity of fluid to flow without needing to increase the diameter of the valve seat 24 or to raise the metal diaphragm from the seat 24 so greatly. In other words, as compared to valves without a ring-shaped groove 28, the metal diaphragm valve 20 has an increased Cv value. It is noted that Cv indicates the ease with which fluid is allowed to flow through the valve.
However, while the prior art metal diaphragm valve 20 has the ring-shaped groove 28 communicating with the outflow path 22, the diameter D1 of the outflow path 22, particularly the diameter of the vertical portion of the outflow path 22 near the bottom of the ring-shaped groove 28, is smaller than the width of the ring-shaped groove 28, such that the flow of fluid is squeezed, increasing the flow resistance. Hence, the flow channel as a whole, running from the valve chamber 23 to the outflow path 22 does not allow fluid to flow at a great flow rate. That is, the Cv value cannot be increased further.
The prior art metal diaphragm valve 20 has another problem. To increase the cross-sectional area of the flow path, two vertical holes 22a, 22b are first bored side by side and then the inside walls are smoothed. But this method of processing outflow path 22 is labour intensive.
Furthermore, because the horizontal width W1 at the bottom of the ring-shaped groove 28 is larger than the horizontal diameter D1 at the top of the outflow path 22, a squeezing phenomenon occurs and the flow path resistance tends to increase.
The present invention has been made in view of the above problems, and it is an object of the present invention to provide a metal diaphragm valve that allows a large quantity of fluid to flow from the valve chamber to the outflow path without difficulty.
The metal diaphragm valve of the present invention comprises a body provided with a valve seat at a bottom face of a valve chamber communicating with an inflow path and an outflow path, a metal diaphragm having an upwardly-bending central region which is provided in the body in such a way that the valve chamber 23 is kept airtight, driving means for allowing the metal diaphragm to rest on the valve seat and for allowing the metal diaphragm to return elastically to its original shape and move away from the valve seat and a ring-shaped groove formed under the valve chamber and communicating with the outflow path, wherein the diameter of the outflow path is made larger than the width of the ring-shaped groove, and the effective cross-sectional area of the regions in which the ring-shaped groove and the outflow path intersect each other is made larger than the transverse cross-sectional area of the outflow path.
Since the diameter of the outflow path is made larger than the width of the ring-shaped groove and the effective cross-sectional area of the regions of intersection between the ring-shaped groove and the outflow path is made larger than the transverse cross-sectional area of the outflow path, the fluid is not squeezed when it flows from the ring-shaped groove to the outflow path, with the resistance of the flow path decreased. This makes it easy for the fluid to flow all the way from the valve chamber to the outflow path and allows a large quantity of fluid to flow. In other words the Cv value that indicates the ease of flowing of the fluid is increased.
It is desirable that the outflow path runs linearly, such that the outflow path and the ring-shaped groove in the depth-direction form a straight line. This allows fluid from the valve chamber to flow linearly from the ring-shaped groove to the outflow path, such that the flow of fluid in the flow path is very smooth.
The outflow path may be slanted at an acute angle in relation to the depth direction of the groove.
That way, the effective cross-sectional area of the regions in which the ring-shaped groove and the outflow path intersect one another is increased such that the resistance to flow from the ring-shaped groove to the outflow path is decreased.
The aforesaid acute angle is preferably not greater than 45 degrees. This way, the effective cross-sectional area of the regions where the ring-shaped groove 5 and outflow path 7 intersect one another is increased in relation to the transverse cross-sectional area of outflow path 7 without increasing flow path resistance.
The diameter of the outflow path is preferably 1.5 to 2.5 times as large as the width of the ring-shaped groove, such that a substantial decrease in flow path resistance can be expected and it is easy to form an outflow path.
Furthermore, it is desirable that the top portion of the outflow path communicating with the ring-shaped groove is hemispherical in shape, such that flow of fluid from the ring-shaped groove to the outflow path can be made smooth.
It is also desirable that the ring-shaped groove and the outflow path are connected such that the bottom of the ring-shaped groove is located near to the centre of the hemispherical top portion of the outflow path.